This is a competitive renewal of NIH grant DK31036. This grant is now completing 28 years and a 10-year cycle since receiving a merit extension by NIDDK. Since its inception, the grant has been focused on the insulin receptor, and to a lesser extent IGF-1 receptor, and their signaling capabilities and their alterations in physiologic and pathologic states. Since the last renewal, we have made very substantial progress in understanding the signaling and biological roles of these receptors through both in vitro and in vivo studies. The largest body of studies derived from the use of homologous recombination gene targeting to study the role of the insulin receptor in insulin action in vivo. This has included the use of single gene knockouts of the insulin and IGF-1 receptors; combinatorial homozygous and heterozygous knockouts as polygenic models of Type 2 diabetes; and tissue-specific knockouts using the Cre-lox approach to determine the role of the insulin and IGF-1 receptors in individual tissues in the physiology of glucose and lipid homeostasis and the pathophysiology of diabetes and metabolic syndrome. In addition, we have performed a series of in vitro studies focusing on differential signaling by the insulin and IGF-1 receptors in the actions of insulin and IGF-1. As a result, since the last competitive renewal, this grant has provided support for a total of 90 published papers (including 48 original articles, 26 collaborative articles and 16 reviews). This work has led to development of new hypotheses about the nature of the insulin/IGF-1 signaling network, the contribution of insulin resistance in different organs to diabetes and the metabolic syndrome, as well as new evidence on how tissues communicate with one another in insulin resistant states, a role for insulin signaling in fat in longevity and a role for insulin signaling in the brain in neurodegeneration. In unpublished studies, we have also developed data on the role of the insulin receptor in brain in the control of CNS cholesterol metabolism and a novel role of signaling from the unoccupied insulin and IGF-1 receptors in control of apoptosis which appears to be kinase independent. The specific aims for the next grant period are: 1) Explore the role of insulin and IGF-1 signaling in increased longevity, stress resistance and mitochondrial metabolism in mice with selective insulin resistance in fat or brain. 2) Study the role of insulin signaling in the brain on regulation of brain cholesterol metabolism and the relationship of CNS insulin resistance and altered cholesterol metabolism to neurodegeneration. 3) Determine the nature of tyrosine kinase independent signaling by the unoccupied insulin and IGF-1 receptors involved in control of apoptosis. 4) Define the differential nature of insulin and IGF-1 receptor signaling in vivo by creation of a new generation of mouse models in which the insulin receptor is replaced by knocking of the IGF1 receptor or a chimeric insulin/IGF-1 receptor to produce mice and cell lines that express each receptor or chimeric receptor in the tissue and temporal pattern of the other receptor.